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      1 /*
      2  * Copyright  2016 Intel Corporation
      3  *
      4  * Permission is hereby granted, free of charge, to any person obtaining a
      5  * copy of this software and associated documentation files (the "Software"),
      6  * to deal in the Software without restriction, including without limitation
      7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
      8  * and/or sell copies of the Software, and to permit persons to whom the
      9  * Software is furnished to do so, subject to the following conditions:
     10  *
     11  * The above copyright notice and this permission notice (including the next
     12  * paragraph) shall be included in all copies or substantial portions of the
     13  * Software.
     14  *
     15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
     16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
     18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
     19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
     20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
     21  * IN THE SOFTWARE.
     22  */
     23 
     24 #pragma once
     25 
     26 #include "nir.h"
     27 
     28 /** A helper for placing phi nodes in a NIR shader
     29  *
     30  * Basic usage goes something like this:
     31  *
     32  *     each variable, var, has:
     33  *         a bitset var.defs of blocks where the variable is defined
     34  *         a struct nir_phi_builder_value *pb_val
     35  *
     36  *     // initialize bitsets
     37  *     foreach block:
     38  *         foreach def of variable var:
     39  *             var.defs[def.block] = true;
     40  *
     41  *     // initialize phi builder
     42  *     pb = nir_phi_builder_create()
     43  *     foreach var:
     44  *         var.pb_val = nir_phi_builder_add_value(pb, var.defs)
     45  *
     46  *     // Visit each block.  This needs to visit dominators first;
     47  *     // nir_foreach_block() will be ok.
     48  *
     49  *     foreach block:
     50  *         foreach instruction:
     51  *             foreach use of variable var:
     52  *                 replace use with nir_phi_builder_get_block_def(var.pb_val)
     53  *             foreach def of variable var:
     54  *                 create ssa def, register with
     55  *     nir_phi_builder_set_block_def(var.pb_val)
     56  *
     57  *     nir_phi_builder_finish(pb)
     58  */
     59 struct nir_phi_builder;
     60 
     61 struct nir_phi_builder_value;
     62 
     63 /* Create a new phi builder.
     64  *
     65  * While this is fairly cheap, it does allocate some memory and walk the list
     66  * of blocks so it's recommended that you only call it once and use it to
     67  * build phis for several values.
     68  */
     69 struct nir_phi_builder *nir_phi_builder_create(nir_function_impl *impl);
     70 
     71 /* Register a value with the builder.
     72  *
     73  * The 'defs' parameter specifies a bitset of blocks in which the given value
     74  * is defined.  This is used to determine where to place the phi nodes.
     75  */
     76 struct nir_phi_builder_value *
     77 nir_phi_builder_add_value(struct nir_phi_builder *pb, unsigned num_components,
     78                           unsigned bit_size, const BITSET_WORD *defs);
     79 
     80 /* Register a definition for the given value and block.
     81  *
     82  * It is safe to call this function as many times as you wish for any given
     83  * block/value pair.  However, it always replaces whatever was there
     84  * previously even if that definition is from a phi node.  The phi builder
     85  * always uses the latest information it has, so you must be careful about the
     86  * order in which you register definitions.  The final value at the end of the
     87  * block must be the last value registered.
     88  */
     89 void
     90 nir_phi_builder_value_set_block_def(struct nir_phi_builder_value *val,
     91                                     nir_block *block, nir_ssa_def *def);
     92 
     93 /* Get the definition for the given value in the given block.
     94  *
     95  * This definition will always be the latest definition known for the given
     96  * block.  If no definition is immediately available, it will crawl up the
     97  * dominance tree and insert phi nodes as needed until it finds one.  In the
     98  * case that no suitable definition is found, it will return the result of a
     99  * nir_ssa_undef_instr with the correct number of components.
    100  *
    101  * Because this function only uses the latest available information for any
    102  * given block, you must have already finished registering definitions for any
    103  * blocks that dominate the current block in order to get the correct result.
    104  */
    105 nir_ssa_def *
    106 nir_phi_builder_value_get_block_def(struct nir_phi_builder_value *val,
    107                                     nir_block *block);
    108 
    109 /* Finish building phi nodes and free the builder.
    110  *
    111  * This function does far more than just free memory.  Prior to calling
    112  * nir_phi_builder_finish, no phi nodes have actually been inserted in the
    113  * program.  This function is what finishes setting up phi node sources and
    114  * adds the phi nodes to the program.
    115  */
    116 void nir_phi_builder_finish(struct nir_phi_builder *pb);
    117